Electrically heated windows

ABSTRACT

A novel silk screen, a novel process of making it, and a novel use in the technology of heating flat bodies such as automobile and factory windows. The new screen is characterized by slits of differential width, depth, or both which permit the deposit of lines of differential section. This has a special significance when the lines are composed of electrical conductors of resistance type of which the resistivity of a part is determined by its section. The process involves a method of making the new type of silk screen which is extremely flexible and permits the construction of screens, the slits of which are differential as to width and differential as to thickness. The process has been achieved by a novel process which relies upon basic techniques already known to the silk screen art, such as the making of emulsions of proper conductivity for heating lines, the technique of preparing the emulsions, and the technique of dissolving those portions which must be removed to form the slits constituting the design. The invention also involves the novel windows which bear designs of differential resitivity producing different temperatures in different parts. These advantages are particularly important in the automotive field but are equally so in factories where overhead windows can be kept clear to furnish light even during snowy weather. Other objects, novelties, and advantages of the invention will be apparent after the reading of this specification.

tlite States Baum et a1.

atent 1191 [451 Dec. 3, 1974 1 1 ELECTRICALLY HEATED WINDOWS [73] Assignee: Saint-Gobain Industries, Neuilly sur/Seine, France [22] Filed; Apr. 9, 1973 [21] Appl. No.: 349,431

Related US. Application Data [62] Division of Ser. No. 17,182, March 6, 1970,

abandoned.

[30] Foreign Application Priority Data Mar. 7, 1969 Germany 1911555 Mar. 8, 1969 Germany 1911561 [52] US. Cl 219/522, 101/127, 117/21'2, 219/203, 219/543, 338/217, 338/309 [51] Int. Cl. H051) 3/06 [58] Field of Search 101/127, 128.2, 128.3,

[56] References Cited UNITED STATES PATENTS 2,054,914 9/1936 Simpson l01/l28.3

2,175,364 10/1939 Rugonstein 101/127 2,557,983 6/1951 Linder 219/543 2,562,676 7/1951 Morton eta1..... 101/128.2

2,569,773 10/1951 Orr 219/543 2,689,803 9/1954 Ackerman 117/37 2,715,668 8/1955 Booker et a1. 219/543 X 2,813,960 11/1957 Egle et a1 219/345 2,859,321 11/1958 Garaway.... 219/543 X 3,095,492 6/1963 Gaiennie.... .1 338/217 X 3,245,023 4/1966 Schmidt 338/211 3,246,598 4/1966 Satonick.... 101/128.3* 3,288,983 11/1966 Lear, Sr. 219/522 3,299,389 1/1967 Vercesi eta1..... 338/217 X 3,313,920 4/1967 Gauez 219/522 3,329,526 7/1967 Daily et a1. 117/227 3,336,465 8/1967 l-lurko 338/217 X 3,336,558 8/1967 Wright 338/217 3,384,931 5/1968- Cochran et a1. 425/128 3,553,833 l/1971 Jochim et a1. 219/203 X FOREIGN PATENTS OR APPLICATIONS 841,868 2/1939 France.... 219/203 1,062,708 8/1959 Germany 219/203 1,209,777 10/1970 Great Britain 219/203 Primary Examiner-Volodymyr Y. Mayewsky Attorney, Agent, or Firm--Pennie& Edmonds ABSTRACT A novel silk screen, a novel process of making it, and a novel use in the technology of heating flat bodies such as automobile and factory windows. The new screen is characterized by slits of differential width, depth, or both which permit the deposit of lines of differential section. This has a special significance when the lines are composed of electrical conductors of resistance type of which the resistivity of a part is determined by its section. The process involves a method of making the new type of silk screen which is extremely flexible and permits the construction of screens, the slits of which are differential as to width and differential as to thickness. The process has been achieved by a novel process which relies upon basic techniques already known to the silk screen art, such as the making of emulsions of proper conductivity for heating lines, the technique of preparing the emulsions, and the technique of dissolving those portions which must be removed to form the slits constituting the design. The invention also involves the novel windows which bear designs of differential resitivity producing different temperatures in different parts. These advantages are particularly important in the automotive field but are equally so in factories'where overhead windows'can be kept clear to furnish light even during snowy weather. Other objects, novelties, and advantages of the invention will be apparent after the reading of this specification.

4 Claims, 1 Drawing liigure ELECTRICALLY HEATED WINDOWS This is a division of application Ser. No. 17,182, filed Mar. 6, 1970, now abandoned.

The invention concerns the manufactureof an electrically heated window carrying on the surface of the glass linear resistance bands of metallic composition deposited by serigraphy and baked, which preferably presents in a certain zone of the field of vision a resistance per unit length higher than exists outside of that fundamentally distinguished in that -it is provided with resistance bands which may be of any chosen design, e.g. approximately parallel, and which are usually less than 0.8 mm. and preferably about 0.6 mm. in width, and of which the conductivity is essentially due to a layer of metallic ink deposited in a single impression. According to a development of the invention, at least some of these bands present several zones of different zone, inorder to establish a principal field of vision tissue. The design which is to be reproduced is then projected onto this film by exposure to light through a photographic transparency of full size that is placed in direct contact with the photosensitive layer. Luminous rays of short wave length expose the photosensitive layer with the exception of the masked parts, from which the emulsion is later removed with hot water to form the stencil. Heated windows of this type are used particularly in automobiles, to which they give good visibility by preventing the formation of condensate or ice, or by melting icewhich has formed.

The resistance bands themselves should be sufficiently thin not to obstruct visibility. As a general rule they are. about 0.4 mm. in width. In order for the heating network to be effective it should dissipate a power of about 4 watts per one hundred per square centimeters. Being given the voltages habitually available in automobiles this requires that a certain minimum of conductivity must be imparted to the strips, that is to say a minimum per section. Heretofore it has not been possible to produce adequate sections by depositing the conductive strips through a silk screen because it was not feasible to increase the thickness of the strips while maintaining minimum width, as'explained hereinabove, and because the silk screen technique did not permit the application of a layer of metallic ink of sufficient thickness with the necessary precision. This difficulty has been somewhat reduced by reinforcing the conductive strips by electroplating. Electrically heated windows of that type have been used as the rear windows of automobiles, e.g. as described in French Pat. No. 1,464,585, the increase of heat within the principal field of vision having been obtained by thickening the resistance strips, exterior to the principal field, by electroplating, which simultaneously produces the differential conductivity desired. That process goes in several steps, first depositing a conductive ink including silver particles and vitreous frit on the glass; secondly baking it; thirdly, electroplating it in a double operation by depositing a conductive layer of copper, and covering it with a protective layer of nickel which improves the appearance but plays a secondary role as to conductibility. v

A principal object of the present invention is to produce a heated window of this kind by eliminating the electrodeposited copper, which reduces the cost of manufacture. The elimination of the electrodeposited conductive layer also permits the elimination of the protective layer of nickel, although the use of the latter heating effect between which the unitary difference of electrical resistance is obtained by establishing difference in section of the heating stripes.

The invention has, therefore, as another object a silk screen photographic process which accomplishes the deposition of resistance strips of chosen, differing section in a single operation, producing the desired conductibilities by the sole use of printed lines. This result is preferably achieved by the successive deposition of several photosensitive layers one upon the other, the later being deposited after drying the earlier. Thus one makes the photographic screen as thick as required, so as to confer an increased depth upon the grooves corresponding to the heating grid. This permits the deposition of the conductive paste to a thickness adequate to achieve the heating effect desired in a particular locati0n.,ln general the thickness of each layer deposited to build up thickness should not exceed 50 pm.

In one, mode the hardening by exposure to light through the transparency is carried out in one exposure after obtaining the selected total thickness of the film. This mode of execution is appropriate to the production of a photosensitive layer composed of a small number of superimposed strata; but if the total thickness exceeds a certain value, the absorption of light rays at the dow of the type described in this invention is therefore surface of the layer prevents the deeper layers from hardening properly. If it is desired to still further increase the total thickness of thelayer, it is possible, according to another mode of the invention, to so operate that after depositingand drying a first layer composed of one or more strata and exposing this layer through the transparency, after washing and drying, a second analogous layer is deposited ,and exposed through the same transparency, taking care to superimpose the contours exactly, and so on layer by layer until one has achieved the desired thickness of film.

The screens produced by the process of the invention are particularly useful in the one-stroke manufacture of heated windows which have zones between which the resistance of the conductive lines per unit length varies, enabling the maker to manufacture windows of larger sizes than was heretofore practical because the larger part of the heating power is dissipated in particular zones, for instance that of the primary fields of vision.

of vision are covered vvith a photosensitive layer of increased thickness during manufacture sothat the thickness of the metallic paste is increasedin the corresponding regions of the windows. During the manufacture of these screens the slits may be constructed with a width, inside the principal field of vision, which is smaller than their width outside the field.

The screens of the invention are constructed so that the slits provided for the passage of ink have a section proportional to the local conductibility desired in that portion of the window to which it is applied varying from zone to zone as desired.

The invention provides several methods of producing a photographic image having the desired properties from transparency, sometimes called a model, having 7 lines of constant width throughout its length, a construction which is highly desirable if one is to achieve without excessive difficulty the exactitude which is so necessary to a satisfactory result.

According to the. first mode'of the invention one produ'c'es a photographic screen having slits of identical width but different depth. In this mode it is the thickness of thephotosensitive layer deposited upon the tis sue which differs, being greater in the-end regions than vin the central portion which constitutes the main field of vision. When the ink is applied to the window through the stencil, slits in the screen, the lines have a thickness corresponding to the contiguous portions of the slits. The processmay thus be carried out in a single step, the, sensitive emulsion being laid upon the tissue as a stratum or as strata of different thickness. The

thickness thus provided can be increased only within larger limits, it is within the contemplation of the invention to deposit several strata one after the other, each time after having-dried the preceding strata. In this method of making the screen the thickness of the sensitive layer can be increased at will but, because of the absorption of light in the upper thickness, too great a thickness'will not harden at the bottompTo avoid this difficulty one deposits several photosensitive layers one upon another but with exposure to light between deposits, developing them in turn. During the exposure of each successive layer the transparency should be returned to its'plac'e on the screen with precision so as to conform exactly to the pattern. The process can then be repeated until the screen has received the desired thickness. I i

To produce an image having bands of variable width, another mode is used according to the invention in which a transparency is employed which has opaque lines of constant width but, to reduce the width of the lines in the principal field during the fixation of the sensitive'layer, the lines in the principal field are either exposed lo ng'er to the light or are exposed to more intense light; The operation of this process appea'rsto derive from the fact'that as the exposure is increased a larger quantity of light diffuses along theedges of the lines masked'by the transparency, which allows the hardening of the photosensitive layer even into the edges of the masked areas. By selecting the quantity of exposure it is possible to change the degree to which the lights are progressively reduced in size within their given limits. If it is desired to produce a greater reduction of size of the lines than can beobtained by a variation of the quantity of exposure, one may, within the scope of the invention, interpose a transparent, thin interlayer between the transparency and the sensitive layer during the exposure and thus provide that the lines of the transparency which interrupt the light are somewhat removed from the sensitive. layer so that some of the rays of light are diverted into the-masked area. By choosing the thickness of the interlayer it is possible to impart selected width to the lines in the regions affected at will and with great precision.

lt is also to be understood that the several modes discussed above may be combined one with another, which permits greater variation and distribution of resistivity according to a preconceived plan.

The single FIGURE of the. drawing schematically illustrates, in perspective, without respecting proportions, the manufactureof a heated window in accordance with the best mode .ofthe invention.-

sponds to the principal field of vision. The transparency 1 is placed upon the insert 9 and the screen is exposed to ultraviolet rays anddeveloped in the way which has been described hereinabove. The grid 2 is thus transferred to the screen which has the appearance schematized in the FIGURE. The stencil plate is thus made impermeable to the metallic ink except in those zones which were masked by the grid 2, 3, 4, duringthe exposure to ultraviolet, of which lines 13 correspond to lines 3 and lines 14 correspond to lines 4. After the exposed plate has been washed withhot water it becomes a stencil attached to the silk, and the lines 13 and,l4 appear as slits free of emulsion, shallow in themedian region 8b, and deeperin theend regions 8a. Because of the warping of light by the irise rt 9. the intermediate parts 14b of the slits l4v are thinner than'the parts 14a. The screen is now ready for use in applying the conductive lines to an automobile windshield 20. The frame 5 is lowered until the sli k screen is in accurate position on i the surface of the windshield and the slits l3 and 14 are completely filled with ink by strokes of the doctor blade (not shown) which serves to apply the ink to the glass through the screen, In this way the sections of the conductive heating lines on the windshield vary from one part to another of their length. This produces bus bands 23 connected by parallel heating lines 24 of which the section i's greater at the ends 244 than in the midportions 24b resulting,.during the flowof current from the automobile battery, in the development of the highest temperature in theiportions24b, a lower temperaturein 24a,v and aleast temperature in the bus bands 23, it being observed that the bus bands are illustrated as of greater section than the portions 24a which are in turn of greater section than portions 24b of the grid. t

This produces the highest temperature in the main field of vision in the center of the windshield, a median temperature toward the ends of the windshield, and a least temperature adjacent the bus bands;

(EXAMPLE 1 A silk tissue of I threads per centimeter -is mounted on a frame in the usual way and a photosensitive emulsionof standard type is depositedon it by any known technique. For such techniques and such emul-' sions, works on the silk screen can be consulted. The emulsion is dried. The transparency,carrying lines 0.4

mm..wide arranged in the size and pattern desired on EXAMPLE 2 Preparing a silk screen in the usual way, for instance as in Example 1, but placing a transparent sheet having a thickness of 0.1 mm. between the photosensitive surface and the transparency, an exposure of 3 minutes, and washing in hot water, produces a silk screen which has lines 0.3 mm. wide in the principal fieldand 0.4 mm. wide outside of it. 1

EXAMPLE 3 On the silk tissue of Example l a first photosensitive emulsion is deposited by the use of a doctor blade of the usual type. This layer is hardened in the usual way and upon it is superimposed a second emulsion, which is hardened, and then a third. After hardening and drying the third stratum, the total thickness of the photosensitive layer is about 100 pm. The transparency has a design of which the lines have a width of 0.4 mm. after exposure and formation of the slits by solution in hot water/The screen was used to mark a window, producing lines 0.4 mm. wide which, after baking, had a thickness of pm. The resistance of these lines, when employing a standard composition ofcommerce as de scribed in the first part of this application, had a value from I to 1.5 O/dm.

EXAMPLE 4 A silk screen-is made according to Example 1 but, after removal'ofthe transparency and development, the screen is again coatedwith three successive layers of emulsion and then exposed, attention being paid to obtaining exact superimposition'of the transparency after each layer has been applied. After development the screen produced resistance lines, after baking,'having a thickness of 30 p.m., the resistance of which fell to l Q/dm.

EXAMPLE 5 A silk screen is made as in Example 1 and after exposure, washing and drying of the first photosensitive layer, a second photosensitive emulsion layer is deposited in the region of the principal field of vision only in a very thin and uniform layer. In the other regions of the screen a considerably thicker stratum is applied. In order to carry this out and to produce a layer of equal thickness one may employ a footed plate of which the feet are on the lower surface and of the dimensions desired in the layer. This permits the production of a layer which is precise in its dimensions. After drying that stratum the transparency is put in place in exact register and exposure takes place. The parts not exposed are eliminated by washing and the silk screen is finished in the usual way and is used to produce resistance bands gions the thickness is um. and the resistance less than 1 .Q/dm.

EXAMPLE 6 A silk screen is prepared as in Example 1 and upon the first photosensitive layer is deposited a new photosensitive layer of uniform thickness limited to the principal field of vision, and thicker layers in the regions outside of it. The second layer is dried. After drying, the photosensitive emulsion is about 60 pm. thick in the principal field and about 100%m. in the secondary zones. The transparency is placed upon this screen, the design having lines 0.4 mm. wide. Exposure to ultravioletlight was as in Example 1 and the design is developed by washing with hot water. The reproduction of thisdesign on glass sheets through this screen produced resistance lines which, after baking, had a thickness of 12 pm. in the principal zone and of 20 um. outside it. Their width remained at 0.4 mm., their resistance was 3.4 Q/dm. in the principal field and 1.5 Q/dm. in the remaining parts.

I EXAMPLE 7' A silk screen was made by the process described in Example 6. After exposure, rinsing and drying, a new emulsion stratum of equal thickness in the central zone and thicker in the other zones was deposited/After dryingthe same transparency was put in place and after a new exposure to light the design in the screen was formed in the usual way and the plate was washed and dried. This screen deposited conductive bands which, after drying, had a thickness of 17 um. and a corresponding resistance of 2.3 fl/dm. in the principal field and of 30 um. and l Q/dm. outside of it.

This invention involves a novel silk screen, a novel process of making it, and a novel use in the technology of heating flat bodies such as automobile and factory windows. The new screen is characterized by slits of differential width, depth, or both which permit the depositof' lines of differential section. This has a special significance when the lines are'composed of electrical conductors of resistance type of which the resistivity of having a thickness in the principal field of 17 um. and

an electrical resistance of 2.3 fl/dm, while in the rea part is determined by its section. The process involves a method of making the new type of silk screen which is extremely flexible and permits the construction of i screens the slits of which are differential as to width and differential as to thickness. The process has been achieved by a novel process which relies upon basic techniques already known to the silkscreen art, such as the making of emulsions of proper conductivity for heating lines, the technique of preparing the emulsions, and the technique of dissolving those portions which must be removed toform the slits constituting the design. The invention also involves the novel windows which bear designs of differential resistivity producing different temperatures in different parts. These advantages are particularly important in the automotive field but are equally so in factories where overhead windows can be kept clear to furnish light even during snowy weather.

As many apparently widely different embodiments of the present invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments.

What is claimed is:

parallel to each other and having a width and being separated one from the other by a distance so as not to obstruct visibility through said glass sheet, and electrically conductive resistance lines adhered to said'surface and connecting ends of said plurality of lines into a single circuit.

2. A thermal window according to claim 1 wherein said at least some resistance lines consist essentially of said hardened metallic ink. I

3. A thermal window according to claim 1 wherein at the portions of smaller cross-section thereof said at least some linesare narrower in dimension parallel to the surface of said sheet than at the portions of larger cross-section thereof.

4. A thermal window according to claim Iwherein at the portions of smaller cross section thereof said at least some lines are thinner in dimension perpendicular to the surface of said sheet than at the portions of larger cross-section thereof. 

1. A thermal window comprising a smooth-surfaced transparent glass sheet, a plurality of opaque electrically conductive resistance lines of hardened metallic ink adhered to a surface of said sheet, at least some of said lines being of uniform composition along tHe length thereof and having a cross-section which is smaller over a common viewing portion of the length thereof between their ends than over the end portions thereof for increased heating within said viewing portion, said at least some lines extending substantially parallel to each other and having a width and being separated one from the other by a distance so as not to obstruct visibility through said glass sheet, and electrically conductive resistance lines adhered to said surface and connecting ends of said plurality of lines into a single circuit.
 2. A thermal window according to claim 1 wherein said at least some resistance lines consist essentially of said hardened metallic ink.
 3. A thermal window according to claim 1 wherein at the portions of smaller cross-section thereof said at least some lines are narrower in dimension parallel to the surface of said sheet than at the portions of larger cross-section thereof.
 4. A thermal window according to claim 1 wherein at the portions of smaller cross section thereof said at least some lines are thinner in dimension perpendicular to the surface of said sheet than at the portions of larger cross-section thereof. 